In the field of automotive seat recliners continuously variable adjustment has been achieved through "taumel" type gearing actuated, in the case of manual adjustment, by rotating a cam through a hand knob which produces a one tooth relative progressive movement between external and internal gears of the taumel mechanism for every revolution of the hand knob. Self-locking friction of the elements produces a satisfactory locked condition for any position of continuous adjustment; however, gross adjustment between extreme positions is relatively slow as compared to the ratchet and pawl type of recliner hinges in general use in the United States, such as disclosed in U.S. Pat. No. 4,223,947, wherein a handle actuated cam releases a pawl from engagement with a toothed sector to accommodate rapid postitioning of the seat back whereupon release of the hand lever permits cam locking of the pawl in toothed engagement with the sector. In such hinges adjustment positions are incrementally limited to a single tooth differential in relative sector and pawl positions.
In order to satisfy industry demand for rapid plus finer adjustment than is possible with conventional sector and pawl tooth pitch, various approaches have been tried. Thus, in U.S. Pat. Nos. 4,223,946 and 4,355,846 an additional "translation" linkage has been incorporated to amplify the angular movement of a toothed sector in relation to the angular seat back movement so as to correspondingly reduce the angular displacement of the seat back for a one tooth adjustment in the engagement of pawl and sector. In another case, as shown in U.S. Pat. No, 4,295,682 an exceptionally fine tooth pitch has been accommodated through use of a special clamping action in the cam actuated mechanism for more positively resisting tooth disengagement through deflection of the inter-engagement elements.
While some improvement in fineness of adjustment has been achieved by such means, the ideal of true continuously variable adjustment combined with rapid gross adjustment to desired seat back position has never heretofore been satisfactorily achieved. Various attempts at friction locks have never been able to withstand life testing under impact loads, which safety standards have required, within space and cost confines involved in the parameters of seat hinge design.